Utilization of cold-rolling oil sludge via iron ore sintering co-processing technology: A strategy for industrial-scale disposal of hazardous solid waste

The steel cold-rolling process generates a considerable amount of cold-rolling oily sludge (CROS), which has been classified as hazardous waste in Chinese "National Hazardous Waste List" due to its significant impact on human health and the environment. This study developed a co-processing method using iron ore sintering technology to achieve harmless disposal and resource utilization of CROS. TG-DSC-MS, temperature-dependent SEM, XRD and XPS experiments were conducted to study the thermal decomposition behavior and phase transformation of CROS. Results showed that incineration temperature had minimal impact on residue composition, with Fe 2 O 3 , MgO, and SiO 2 content in CROS remaining above 44.9%, 33.2%, and 2.7%, respectively, making it suitable for use in sintering. Sintering pot trials showed that adding 0.5 wt.‰ CROS maintained a tumbler index above 68% and kept sintering speed within normal ranges. Heavy metal leaching values were below the national limits (GB 5085.3-2007), indicating no leaching risk. Industrial trials confirmed that adding 0.5 wt.‰ CROS to the sintering feed did not adversely affect finished sinter performances, sintering conditions and physicochemical properties of the dust. The Fe 2 O 3 and FeO contents of sinter exceeded 57% and 8%, respectively, showing good applicability for BF smelting. Moreover, main pollutant emissions concentration of dust, sulfur dioxide (SO 2 ), nitrogen oxides (NO X ), and dioxin in sintering flue gas were 14.74 mg/m 3 , 120.51 mg/m 3 , 253.15 mg/m 3 and 0.188 ng I-TEQ/m 3 , respectively, lower to the emission standard limits set by GB 28662-2012 (50 mg/m 3 , 200 mg/m 3 , 300 mg/m 3 and 0.5 ng I-TEQ/m 3 ). In addition, flow rate, particularly dioxin formation pathways, remain similar to the basic case without CROS addition in the sintering feed. This study presents a feasible and environmentally friendly solution for the safe disposal and resource utilization of CROS within the iron and steel industry, with the potential to enable on-site disposal of CROS.